The invention relates to an optical microelectromechanical device, and in particular to an optical MEMS device with improved suspension.
U.S. Pat. Nos. 6,574,033, and 6,794,119 disclose optical microelectromechanical systems (optical MEMS) and micro-opto-electromechanical systems (MOEMS) devices comprising arrayed floating reflective members to modulate required images by interference.
FIG. 1A shows a conventional optical MEMS device, and FIG. 1B is a cross-section of section a-a in FIG. 1A. In FIGS. 1A and 1B, the conventional optical MEMS device 10 comprises a plurality of conductive wires 13 disposed on a glass substrate 12 with a dielectric layer 14 overlaid thereon. A plurality of reflective members 18 is supported by a plurality of edge supporters 16 and inner supporters 17, suspended from the dielectric layer 14 by a predetermined gap g. The conductive lines 13 are perpendicular to the reflective members 18, and the overlapping areas define a plurality of pixel areas. The edge supporters 16 of the conventional optical MEMS device 10 are located between adjacent pixel areas, crossing the boundaries thereof, such as the edge supporters 16 between pixel areas 11a and 11b in FIG. 1A. The shape, size number and profile of the inner supporters 17 within pixel areas may be different as shown in FIG. 1A to provide proper support at the center of each suspended reflective members 18.
The edge supporter 16 and inner supporter 17 are formed by residual macromolecular materials and with horizontal extending top portions 162 and 172 connect the reflective member 18 to improve adhesion therebetween and distribute stress when the reflective member 18 becomes deformed.
As shown in FIG. 1B, a specific wavelength λ1, for example, is constructively enhanced by interference and reflected, with all other wavelengths destructively eliminated by interference when a light beam with multiple wavelengths λ1, λ2, . . . , λn impinges on the reflective member 18 through the glass substrate 12. The wavelength of the constructive interference depends on the gap g between the dielectric layer 14 and reflective member 18. Furthermore, the reflective member 18 becomes deformed and descended, attaching to the surface of the dielectric layer 14 as shown in FIG. 1B, when an external actuating current is supplied to the conductive layer 13. Accordingly, the reflectivity of the optical MEMS device 10 is reduced, acting as a “dark” state. Thus, the conventional optical MEMS device 10 with arrayed display units is capable of displaying required images according to external control currents.
FIG. 2 is a cross-section of section b-b in FIG. 1A before removal of the sacrificial layer 15. As shown in FIG. 2, corresponding to FIG. 1A, a plurality of openings 152 perpendicular to the dielectric layer 14, is first defined on the sacrificial layer 15 and filled with a photoresist or apolymer therein, forming edge supporters 16 and inner supporters 17.
The conventional optical MEMS device 10, however, does not provide protection to the top end connecting the reflective member 18 of each edge supporters 16. The exposed portion of each edge supporter is easily damaged by etchants or solvents during definition of the reflective members or removal of the sacrificial layer, therefore reliability of the device 10 may reduce.